How can one find out if the fetus has a thalassaemic trait?

Answered by: Dr Shirish Kumar | Haematologist, WHO, Geneva

Q:I want to know regarding the probability of having a thalassaemic child from both parents having traits of thalassaemia. You said earlier that 1 out of 4 is the chance of beta thalassaemia major if a child is born from two minor thalassaemia traits of parents. My fetal Hb is 6.4 while that of my wife is 4.6. In this case, if our child is born, how would we know that our child is a major or minor thalassaemia child. Moreover, in order to know the same, when can we know i.e. during which month of pregnancy? Is it proper to know like that? Otherwise should we go for the child and leave it to the Almighty for the result or is it better to stop planning for pregnancy. Many such queries are popping in my mind. I would be grateful to you if you can please guide me.

A:Prenatal DNA testing is available and the decision to perform prenatal diagnosis in parents known to be at risk for having a child with thalassaemia is complex and is influenced by factors like religion, culture, education, and the number of children in the family.
Molecular diagnostic tests can precisely determine if a mutation is present any time after approximately 8 weeks of pregnancy. The DNA can be obtained from amniocentesis (14-20 weeks) or by chorionic villus sampling (8-10 weeks). The DNA is then amplified using the polymerase chain reaction technique and then analysed for the presence of the thalassaemia mutation using a panel of oligonucleotide probes corresponding to known thalassaemia mutations in a given community. Fetal blood sampling for Hb chain synthesis can also be done at 18-22 weeks of pregnancy but this procedure is not as reliable as DNA analysis sampling methods.
Any medical centre having a genetic laboratory will have these facilities. You should consult a genetic counsellor who will address the genetic risks and the risks involved in testing so that you can make an informed and intelligent decision concerning the procedure.